1. Field of the Invention
This invention relates to a fluid level measuring system for machines.
2. Description of the Prior Art
It is quite common for machines that have rotating and/or reciprocating elements to use a variety of fluids. These fluids can serve to lubricate, transfer heat, or any number of other uses. The level of these fluids can be critical to the operation of a machine. For example, if the level is too low then friction and inadequate heat transfer can damage the machine. If the level is to high, then the heat transfer may not be accomplished fast enough thus exposing the machine to overheating.
A major difficulty exists in measuring the level of fluid. Machines can incorporate elements that retain fluid within components of the machine when the machine is operating, temperatures and pressures within the machine can vary and thus effect the fluid level, and the fluid may interact with the air such that bubbles may exist within the fluid. These and other variables make it hard to obtain a precise measurement of the fluid in a machine. For abetter understanding of these issues a transmission is used as a representative machine.
Finding the level of transmission fluid has always posed a significant problem. To better understand this problem, it is necessary to discuss some relationships between the transmission and the transmission fluid. To begin with, transmissions have a pan that collects, transmission fluid. Fluid circulates through the transmission and the pan while the transmission is operating at a rate that is dependent upon factors such as the transmission gear setting and speed. When a transmission is not operating, fluid is drawn into the pan by the force of gravity. However, not all the fluid will drain into the pan. The transmission components have recesses, grooves, and crevasses that retain fluid. As a result, any reading of a transmission fluid level as measured relative to the bottom of the pan while the transmission is not operating does not include the fluid housed in the components and is thus not accurate.
Likewise, when a transmission is operating the fluid is dispersed throughout the working parts of the transmission with less than all of the fluid being in the pan. Naturally, this leads to a reading, e.g. via an electronic dipstick, of a fluid level which does not account for the transmission""s disbursed fluid while the transmission is operating. To compound this problem the volume of the transmission fluid depends upon the operating temperature of the transmission. When the temperature is high, the fluid expands and there is a larger volume of fluid. These situations create a problem in accurately reading the transmission fluid level and thus obtaining information as to the adequate level or fill of transmission fluid.
It is well recognized in the art that problems exist when the fluid for a transmission in a motor vehicle is not at, or near, an optimum level. Improper levels of fluid can cause damage to the transmission in several ways. If the fluid level is low, then the components come into contact and excessive mechanical wear results. If the fluid level is high, then the heat generated by the transmission is not adequately dissipated by the fluid and excess thermal stress results on the components.
Transmissions are expensive to replace and can require that a vehicle, such as a bus or a truck, be taken out of service for what may amount to an extended period of time. Such a service procedure can reduce the profitability of an organization, further compounding the problem.
This problem can be alleviated by knowing the operational transmission fluid level and correcting any improper level conditions before excess wear is experienced. One method of correcting this problem appears in U.S. Pat. No. 4,869,346 to Donald Nelson. In that patent, the level of the engine lubricating oil is determined by a signal frogman electronic dipstick. The fluid level is transmitted to a processor that determines if new oil should be added or removed from the system and controls such addition and/or removal.
While this method is useful in monitoring the time between repairs, it has several shortcomings. If the motor vehicle, such as a bus, is operating on an incline or experiencing frequent stop and go motion then the dipstick may not accurately reflect the fluid-level. Additionally, the processor is not compensating the readings to reflect changes in the apparent oil level caused by thermal expansion or an irregular oil pan shape. This can result in a situation where fluid is added or removed when it is unnecessary to do so. The adjustment of the fluid level by this method is therefore not optimal. Furthermore, the operator is not apprised of the fluid level as determined by the processor or the dipstick.
Another patent by Nelson (U.S. Pat. No. 5,390,762) attempts to calculate the operational transmission fluid level by averaging a number of fluid level readings throughout the transmission. This accounts for any orientation of the engine. However, the speed of the engine can effect the apparent oil level.
At high speeds, the fluid as measured may be lower than at low speeds and the readings may not accurately reflect the fluid level. An average reading may trigger a change in the fluid level that is not necessary. Another drawback is that the placement of numerous fluid level sensors is expensive. A number of access ports must be provided in the transmission to receive the sensors. These openings must be drilled or provided by a similar means and must be leak proof. This is time consuming, expensive, and may result in damage to the transmission if not performed properly. Also, the fluid level is not displayed to the operator.
Another attempt to address the fluid level problem appears in U.S. Pat. No. 5,970,942 to Koeberlein et al and U.S. Pat. No. 5,881,688 to Graham et al. These patents are directed to an apparatus to replace engine lubricating oil based upon the fuel flow of the vehicle. In effect, the engine lubricating oil is continuously replaced but increased during periods of increased fuel consumption. This is referred to as a response to the engine s operating severity value.
The Graham patents do not take into account the operational oil level when changing the oil. As with the Nelson patents, the Koeberlein and Graham patents do not take into account such variables as oil temperature, idle speed or irregular pan shapes to arrive at an operational engine oil level. Nor do the patents anticipate or address the ability to display the operational engine lubricating oil level.
The present invention addresses a fluid level measurement system for a machine for determining an operational fluid level. A fluid level sensor within the machine provides the system with a fluid level signal that reflects the measured fluid level. A temperature sensor within the machine provides the system with a temperature signal. A first data storage device retains the measured fluid level and measured fluid temperature data. A second data storage device contains data for a range of recommended fluid levels based upon a variety of fluid levels and fluid temperatures, which can be obtained from sources such as the manufacturer or through controlled dynamic measurements.
A processor compares the measured sensor values retained in the first memory storage device to data in the second memory storage device. Once the measured values are matched with corresponding values in the second data storage device, then the operational fluid level can be identified, calculated, or estimated.